Sitting in my parents home is a beautiful photograph of my grandfather in his WWII uniform. What makes this photo even more interesting is that someone took the time to watercolor it. I love this look so lets take some older pictures that are already black and white and colorize them.

Zoom in and reduce your brush size to get those edges.
If your color seems a bit too bright like mine does. You can then lower the opacity till it's the shade intensity you're looking for.
http://i302.photobucket.com/albums/nn85/harmonystar1899/tutorials/cm3.jpg

Now make another new layer for each color you use. Color as much or as little as you'd like.

Here's Mine all colorized. Don't forget to add some cheeks in there.
http://i302.photobucket.com/albums/nn85/harmonystar1899/tutorials/cm4.jpg

So pretty. You can also use this technique with photos you've made black & White. Seems kinda redundant to colorize a photo that had color to begin with but you can fix some tone colors that way or do a cute baby doll look. Here's one I did:
http://i302.photobucket.com/albums/nn85/harmonystar1899/tutorials/cm5.jpg

http://i302.photobucket.com/albums/nn85/harmonystar1899/tutorials/cm6.jpg
Can't wait to see what you come up with!